1. Field of the Invention
This invention relates generally to the testing of electrical apparatus, and, in a preferred embodiment thereof, more particularly relates to the electrical testing of printed circuit boards and the like.
2. Description of Related Art
For purposes of production efficiency and economy it is often desirable to simultaneously test the electrical circuitry on both sides of a printed circuit board. As to either side of a given circuit board a conventional method of testing the circuitry thereon is to longitudinally press resiliently deformable, electrically conductive test pins (such as spring loaded "POGO" pins) against a series of test contact points positioned on the selected board side and suitably connected to various predetermined circuit locations thereon. When the circuit board is operatively connected to an input voltage source, these pins function to conductively interconnect the test contact points on the board to a suitable test circuit connected to the pins and operative to receive and analyze the various electrical test output signals picked up by the pins at the test contact points.
While at first glance this appears to be a rather simple, straightforward electrical test procedure, it is well known that it is subject to a variety of primarily mechanical problems. For example, in order to operatively engage and compress the pins against the test contact points it has been common practice to exert a vacuum force directly against the circuit board to be tested to draw the board into operative contact with the pins.
To accomplish this, the board must be enclosed within a vacuum chamber which also encloses the pins. This typically prevents probe access to the pins during testing, and also hides both the circuit board and the pins from view during testing. There is accordingly no reliable way to verify that the pins are maintained in precise perpendicularity with the circuit board as the pins contact the test points and are longitudinally compressed against them. If such pin/board perpendicularity is not maintained, the pins can be bent or broken, and can be undesirably caused to slide along their associated test contact points.
It is also common practice to use rigid "standoff" members in conjunction with the test pins to contact the circuit board and limit the vacuum-forced movement thereof toward the pins in order to controllably limit the pin compression or "stroke". Using this conventional vacuum drive approach it is difficult to verify whether proper contact is being made between the standoff members and the circuit board. If no such contact is made, the test pin/board contact may be insufficient to provide adequate test results. On the other hand, if the circuit board becomes cocked (thus causing an uneven contact between the stand off members and the board), board damage can occur.
Another problem associated with exerting a vacuum force directly on the circuit board to draw it against test pins is that this approach requires that the board be of an essentially nonperforate construction so as not to appreciably interfere with the vacuum being drawn beneath the board. In the case of perforated or substantially porous boards, this direct vacuum approach is typically not feasible.
Various proposals have been made with a view toward eliminating the vagaries and problems associated with direct vacuum-induced contact between the test pins and the circuit board by mechanically driving the circuit board into contact with a set of test pins. This mechanically-induced contact between the board and test pins is typically achieved by pivotally moving the test pins into engagement with the circuit board, or vice versa. Such pivotal movement, however, can easily cause the pins to non-perpendicularly engage the board test points and cause pin damage and sliding similar to that encountered in vacuum drive systems.
Alternatively, various mechanically driven test systems have previously been proposed in which a more direct movement of the circuit board and test pins toward each other is achieved. However, these systems tend to be relatively complex, and provide only very limited access (if any) to the pins during the actual testing of the circuit board.
Thus far, this background discussion has been directed to the problems, limitations and disadvantages associated with conventional circuit board test systems designed to electrically test only one side of a given circuit board at a time. The difficulties in maintaining test pin/circuit board perpendicularly, preventing the pins from sliding along their associated test contact points, preventing board damage due to improper standoff contact therewith, assuring adequate but not excessive test pin contact stroke, and providing access to and visibility of the pins during testing tend to be significantly increased when opposed series of resiliently deformable pins are used to simultaneously contact and test the opposite sides of a given circuit board.
In view of the foregoing, it is accordingly an object of the present invention to provide an improved system, and associated methods, for simultaneously testing opposite sides of a circuit board in which the above-mentioned and other problems, limitations and disadvantages heretofore associated with conventional test systems are eliminated or substantially reduced.